Environmental perturbations can disrupt development by altering both the molecular dynamics as well as tissue- and cell-level mechanics. Specifically, a heat shock administered in early Drosophila embryogenesis can result in developmental defects hours later. This work aims to answer the question of how developmental mechanics are altered by heat shock and how the perturbed mechanics result in developmental defects by focusing on two tissues—amnioserosa and germ band. The amnioserosa and germ band are monolayered epithelial tissues that move in a coordinated fashion through mid-embryogenesis. First, this work focuses on characterizing the mechanics of the amnioserosa and germ band during normal development using techniques such as laser microsurgery, quantification of cell morphology, and particle tracking microrheology. We then show that a heat shock administered in early Drosophila embryogenesis delays development, leads to a spectrum of developmental defects, and disrupts the mechanical integrity of the amnioserosa—catastrophic holes open in the tissue after heat shock. The presence of holes in the amnioserora after heat shock is correlated with defects in mid to late embryogenesis. These results show that a simple non-specific heat shock is sufficient to cause a loss of mechanical integrity of a tissue, disrupting the normal pattern of development.